Send to a friend

"Heartworm symptoms aren’t apparent until the disease is very advanced. For this reason, regular testing is extremely important in dogs."

Dr. Gary Arzem
Newmarket Veterinarian

Heartworm disease is a parasitic disease caused by Dirofilaria immitis. This parasite is transmitted between animals by mosquitoes.

Yes. Ontario continues to be the “hot zone” for heartworm infection in Canadian dogs. The vast majority of diagnoses are made in the southwestern part of the province, but cases are seen all over the province – including cities, suburbs, rural areas, and cottage country.

The life cycle of heartworms is as follows:

• A mosquito bites a heartworm-infected dog and picks up the microfilariae (immature heartworms found in the infected dog's bloodstream)
• During the next 2 to 3 weeks, the microfilariae develop into infective larvae within the mosquito
• When the mosquito feeds again, it can transmit the infective larvae into a healthy dog. The larvae penetrate the dog’s skin and migrate through the tissues, developing over the next few months. Eventually, they reach the dog’s heart.

Yes. Inside a dog’s heart, the worms can grow up to 35 cm long and can cause significant damage to the heart and lungs. Literally hundreds of worms may be found in an infected dog’s heart and the surrounding blood vessels. If left untreated, heartworm disease can result in death.

No symptoms are apparent until the disease is very advanced. For this reason, regular testing is extremely important in dogs. The symptoms of heartworm disease develop gradually over many months, and resemble those of congestive heart failure. In advanced cases, the dog has difficulty breathing, can tolerate only very light exercise, and loses his or her appetite.

While treatment is possible, the drug required to kill the adult worms is very toxic, and must be administered under close veterinary supervision. The dog must be restricted to cage rest until all danger from treatment has passed. It is far easier, safer, and less expensive to prevent heartworm disease than it is to treat it.

It is important to put your dog on a heartworm preventative medication from June until November. The medication is available as an oral monthly tablet or as a topical preparation that is applied monthly. Both are very safe for dogs of all ages. Please call us to discuss the various options. Unless your dog is a young puppy, it is important to have your dog heartworm tested prior to starting him on the preventative medication.

It is very simple. A small sample of blood is collected from your dog and submitted to a laboratory for testing. You will have results within 48 hours.

It is important to confirm that your dog is negative prior to beginning heartworm preventative medication. If your dog is positive and he receives preventative medication, he may experience an adverse reaction as the worms and larvae die. Keep in mind that dogs with heartworm infection do not show symptoms until very late in the stage of disease. Early diagnosis is critical.

Please contact our Veterinary Clinic in Newmarket to inquire about preventing heartworm in your pet. We have flexible appointment times to accommodate your schedule.